While trying to install any module in OpenERP I am getting the below mentioned error:

Integrity Error

The operation cannot be completed, probably due to the following:
- deletion: you may be trying to delete a record while other records still reference it
- creation/update: a mandatory field is not correctly set

[object with reference: Portal employee - hr.employee]

also, there is no install button for leave management, recruitment process, expense management, and employee appraisals. Can anyone please help us in sorting this issue?